Heterodyne receiver



Aug. 4, 1936 R, URTEL 2,049,677

HETERODYNE RECEIVER Filed Dec. 30, 1932 INVENTOR RUDOLF URTEL W ATTORNEYPatented Aug. 4, 1936 omreo stares HETERODYNE RECEIVER l tii dolf Urtel,Berlin, Germany, assignor to Telefunken Gesellschaft fur DrahtloseTelegraphic m. b; H., Berlin, Germany, a corporation of GermanyApplication December 30, 1932, Serial No. 649,484

' In Germany December 9, 1931 a 4 Claims; (Cl. 250-20) My presentinvention relates to superheterodyne receiving systems of the typewherein a single tube is used as a combined local oscillatorfirstdetector.

In the drawing Fig. 1 shows a combined local oscillator-first detectorcircuit of a type known in the prior art,

Fig. 3 shows a combined local oscillator-first detector circuitembodying the invention,

Fig. 2 shows the negative resistance characteristic of the screen gridcircuit of the tube in Fig. 3.

In heterodyne receivers the functions of the first rectifier and theheterodyn-e are often fulfilled by one tube. An arrangement of this kindis shown in Fig. 1 comprising the use of a twin-grid tube I, one grid ofwhich is associated with the input circuit (EF) (for incoming waves),while the sec ond grid circuit contains the circuit (UF) tuned to theheterodyne or local oscillation frequency. This circuit is excited byregeneration (RK) from the plate. From the plate circuit is derived theensuing intermediate frequency (ZF).

Since in the use of screen grid tubes the working conditions that aremost favorable from the viewpoint of amplification coincide with theconditions that are conducive to screen grid secondary emission ofelectrons, and, thus, provided suitable materials are used, to droopingcharacteristics IG=f (VG) (Fig. 2) the negative resistance representedby the screen grid circuit is utilized for wave generation by that, forinstance, the circuit (UF) tuned to the heterodyne wave is in serted inthe lead brought to the screen grid, (Fig. 3). Since in practice thereresult negative resistances of 150,000 ohms (smaller values beingattainable by promoting the elfect), it will be seen that the conditionfor self-excitation ZZR is readily attainable, where Z is the impedanceof circuit UF.

' The circuit scheme shown in Fig. 3 distinguishes itself by greatsimplicity (omission of supplementary feed-back circuit elements), andin addition it offers advantages as regards constancy and shape of thefrequency curve.

The signals in Fig. 3 are impressed on input circuit EF, and the latteris coupled between the control grid and cathode of screen grid tube I.As stated above, the screen grid tube operating conditions are the sameas when the tube operates as an amplifier; hence, the plate P is at apositive voltage, and the screen grid SG is at a positive voltagesubstantially less than that of to the desired local oscillationfrequency, and the intermediate frequency is derived from the circuit ZFin the plate circuit. Suitable by-pass condensers C are employed toby-pass radio frequency currents from the screen grid and platecircuits.

While I have indicated and described one system for carrying myinvention into efi'ect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationshown and described, but that many modifications may be made withoutdeparting from the scope of my invention as set forth in the appendedclaims.

'What is claimed is:

1. A dynatron oscillator-detector comprising a tube having a cathode,control grid, anode and screen grid, both anode and screen grid beingpositive relative to the cathode, the screen grid being sufficientlyless positive than the anode to impart a negative resistancecharacteristic to the screen grid circuit, a tunable signal circuitbetween the control grid and cathode, a tunable local oscillationcircuitin the screen grid circuit adapted to generate local oscillations of adesired connected between the controlgrid and cathode, 3

an intermediate frequency circuit connected to the anode of said tube, atunable local oscillation circuit connected to the screen grid of saidtube, said screen grid being free of any regenerative couplings to anyother electrode circuit of said tube, the anode and screen grid being ata positive potential with respect to the cathode, and the screen gridpotential being sufiiciently less positive than the anode potential tointroduce a negative resistance into the screen grid circuit.

3. In a sup-erheterodyne receiver, a combined first detector and localoscillator network comprising a screen grid tube, a tunable signalcircuit connected between the control grid and cathode, an intermediatefrequency circuit connected to the anode of said tube, a tunable localoscillation circuit connected to the screen grid of said tube, saidscreen grid being free of any regenerative couplings to any otherelectrode circuit of said tube, the anode and screen grid being screengrid potential being sufilciently less than the anode potential toimpart a negative resistance to the discharge space between the cathodeand the screen grid, a signal input circuit connected between the signalgrid and cathode, a local oscillation circuit in the screen grid circuittuned to a frequency differing from the signal circuit frequency by adesired beat frequency, a resonant circuit connected to the anode of thetube and tuned to the beat frequency, said screen grid circuit beingfree of any regenerative cou-- pling with any other electrode circuit ofthe tube.

' RUDoLF URTEL.

